|State|Type|Name|Title|Royal house|From|To|
|---|---|---|---|---|---|---|
|Chu|Sovereign|Huai|King|Mi|328 BC|299 BC|
|Han|Sovereign|Xiang|Marquis|—|311 BC|296 BC|
|Lu|Sovereign|Wen II|Duke|Ji|302 BC|280 BC|
|Qi|Sovereign|Min|King|Tian|300 BC|284 BC|
|Qin|Sovereign|Zhaoxiang|King|Ying|306 BC|251 BC|
|Song|Sovereign|Kang|King|—|328 BC|286 BC|
|Wei|Sovereign|Xiang|King|—|318 BC|296 BC|
|Wey|Sovereign|Si Jun|Marquis|—|334 BC|293 BC|
|Yan|Sovereign|Zhao|King|—|311 BC|279 BC|
|Zhao|Sovereign|Wuling|King|—|325 BC|299 BC|

Question: what is the total number of known vassal states in which their reigning years are known?
Answer: 10